A range camera is an imaging device that can determine the distance from the camera, or range, for each pixel in the captured image. The two-dimensional (2D) pixel coordinates in a captured image along with the measured range at the pixel coordinates determine the three-dimensional (3D) coordinates of a target point in space in relation to the range camera. The resulting data can provide 3D information about targets (objects or scenes) within the image. The information associated with a pixel may correspond to parameters other than range, such as color, temperature, and reflectivity, for example. Thus, the two-dimensional pixel coordinates in a captured image can be associated with multiple parameters that provide information about a scene.
Scanning laser rangefinder type range cameras acquire range to each pixel by measuring time-of-flight of a single laser beam that is scanned over each pixel location in a scene. Typically, the laser beam is mechanically steered in each pixel's direction using rotating elevation mirror and azimuth assemblies. There are disadvantages to the scanning laser rangefinder design, including mechanical complexity (e.g., they typically use spinning mirrors and rotating mounts, which require motors that must be precisely controlled); increased costs and reduced reliability inevitably associated with mechanical design complexity; and relatively long scan times.
Image capture type range cameras capture image data as an array of pixels simultaneously, but known range cameras using this approach suffer disadvantages, such as limited spatial resolution and limited range accuracy, both of which constrain the use of the range data to only those types of imaging and object recognition applications that can accept relatively coarse image and range data, such as robot vision, automatic door openers, or automobile occupancy detectors. One difficulty in using an image capture type range camera for high resolution is that, in addition to increased cost of the higher-resolution sensor array, a higher resolution image requires a smaller pixel dimension, whether it be physically smaller or effectively smaller as a result of optical magnification, and a smaller pixel dimension requires more illumination of the scene to obtain an accurate range reading. There are both practical limits on the amount of illumination that can be provided and safety limits which limit the amount of illumination allowed, thereby avoiding eye damage to those in proximity to the range camera, such as users and bystanders. Laser rangefinders may mitigate the safety issue by generating a pulse of laser light with high peak power but low total energy—a technique that may not give good accuracy results when used with image capture type range cameras, however.
There are a number of important applications for range cameras which, due to the higher data quality or range accuracy requirements, are not being addressed by current range camera technology. Such applications include forensics (e.g., documenting the geometric relationships within a crime scene), construction (e.g., capturing “as built” dimensions of spaces and equipment), security (e.g., creating 3D models for emergency response planning), and entertainment (e.g., creating 3D models for video games or motion picture special effects), to name a few. There are undoubtedly many other possible applications to which a range camera could be applied or adapted but for the relatively high cost of the equipment. Therefore, an unmet need exists for improving the quality of range data obtained from range cameras. Further, an unmet need exists for providing lower cost range cameras useful for rangefinder applications.
Due to the unique nature of a range camera—the ability to record 3D range information of a scene—a user of a range camera may desire to obtain 3D information about an entire room, including not only the three hundred and sixty degree image of the walls but also the areas above and below the camera: the ceiling and floor, respectively. Thus, a range camera should be able to take an unobstructed view of an entire volume. Unfortunately, when using a traditional tilt-and-swivel mount, in which the tilt axis and swivel axis geometrically intersect, the mount itself may obstruct the camera's view of some portion of the scene: the floor, if the mount is atop a pedestal, the ceiling, if the mount is suspended, and so on. Because of this limitation, it may become necessary to obtain image data from two different positions, and perform registration on the collected images. This may require extensive processing time and capability and may introduce additional range errors. Therefore, an unmet need exists for providing a range camera that incorporates a swivel mount that allows the range camera to have an unobstructed view of the entire volume of the scene for which range information is to be collected.
Accordingly, in light of the disadvantages associated with existing laser rangefinders and range cameras, there exists a need for a lower cost range camera with improved range accuracy and spatial resolution and which can obtain range data for an entire volume without obstruction.